Petar Mladenov

Thank you for noticing this issue. We will investigate it and will provide further information whether this is a TreeView specific issue or an issue in the Application logic of the Class Diagram example.
We updated your telerik account points as a thanks for your cooperation.

Petar Mladenov

This issue is previously logged in our system under the name:TreeView: The DefaultImageSource and ExpandedImageSource properties don't work in virtualized tree

If you don not need virtualization (your tree is small and you don't need performance optimization) you can turn it OFF (IsVirtualizing = False) and this will work properly. On the other hand, there is an elegant workaround in MVVM scenarios - do not use these image properties and add Image in the ItemTemplate of the RadTreeView. Then bind its Source to the IsExpanded property and use converter to selected different image sources based on the value of the IsExpanded property.
We think this issue has little priority due to the workaround possible. Furthermore we have to admit that exposing such image properties in our RadTreeView is a mistake in our design. The usual way for such customizations should be ViewModels + ItemTemplates as suggested above.

Petar Mladenov

Just to clarify once again. Performance is optimized in the RadTreeView when the Virtualization is turned ON. But it is perfectly suitable for you to workaround this bug with ItemTemplates with Image and ViewModels containing the SourceUri for the Images. This will work with Virtualization turned ON.

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